With respect to EDSS iron complex and a process for producing the same, for example, an EDDS ferric complex salt and a process for producing the same (JP-A-7-2745 and JP-A-7-29184) and an S,S-EDDS ferric ammonium salt and a process for producing the same (JP-A-8-34764) are known. According to these processes, a combination of EDDS (a mixture of its racemic compound and its meso compound) and an alkali metal hydroxide, or a combination of S,S-EDDS and ammonia is subjected to reaction with iron oxide or iron in an aqueous medium, and the resulting reaction product is oxidized. In addition, a production process comprising mixing an EDDS alkali metal salt and an iron salt dissolved is also known (WO 9811058).
These EDDS iron complexes can be recovered as their solid products by removing water from the aqueous reaction product solution, and then be applied mainly in the field of photographic treatments. Embodiments of applying such a solid treating agent are disclosed in, for example, JP-A-7-295162.
On the contrary, JP-A-10-1660 and JP-A-10-231469 disclose descriptions on improvements of caking properties (consolidating properties) of EDDS iron complex and S,S-EDDS iron complex, respectively.